The present invention relates to exhaust emission control apparatus and method for a direct-injection and spark-ignition type internal combustion engine. More particularly, the present invention relates to a temperature rising technique for early activating an exhaust purifying catalyst provided in an exhaust passage.
There is an internal combustion engine which performs a lean burn by injecting fuel directly into a cylinder from a fuel injection valve and then forming stratified air-fuel mixture within the cylinder at the time of a spark-ignition combustion. Such an internal combustion engine can reduce fuel consumption specifically under a low or middle load condition. Moreover, some earlier technologies with respect to the above-mentioned direct-injection and spark-ignition type internal combustion engine, have been proposed to accelerate the activation of the exhaust purifying catalyst during a cold start and a warm-up process of the engine.
A Japanese Patent Application Provisional Publication No. H10(1998)-169488 published on Jun. 23, 1998 exemplifies a previously proposed technique to promote the activation of the exhaust purifying catalyst. In this technique, an incomplete combustion substance CO (carbon monoxide) is produced by causing a local air/fuel ratio around an ignition plug to be over-rich, when the exhaust temperature rise is required. Thereby, remaining oxygen within the cylinder which has not been associated with the combustion, reacts with the produced CO after a main burning.